The data is stored only for 30 days, as well as the recentchanges thing. The patrolled flag (together with bot flag) is stored only in recentchanges table (stored for 30 days) and not in revision table (stored for indefinite amount of time). And why not? Too much data.

In T200086#4441530, @Urbanecm wrote:

The data is stored only for 30 days, as well as the recentchanges thing. The patrolled flag (together with bot flag) is stored only in recentchanges table (stored for 30 days) and not in revision table (stored for indefinite amount of time). And why not? Too much data.

Each revision is stored somewhere in the database. So, could a tag be too heavy to be stored as well for each edit?
I understand, nonetheless, the need to keep the data stored as reduced as possible.

However, Recent changes could be kept more than 30 days. For en.wikipedia, perhaps you don't want that, but for small wikis it shouldn't be harmful (and imho, to make this even less harmful, edits made by bots could be removed if older than 30 days—but it's up to MediaWiki devs).